i) Field of the Invention
The present invention relates to a combined magnetic head for carrying out a recording and a reproducing of magnetic information against a plurality of data tracks of a magnetic recording medium For use in a magnetic recording and reproducing apparatus such as a floppy disk drive, a VCR (video cassette recorder) or the like, and a producing method of the combined magnetic head.
ii) Description of the Related Arts
FIG. 17 shows a combined magnetic head of a tunnel erase system mounted on a conventional FDD (floppy disk drive), as disclosed in "All About Floppy Disk Drive", by Shoji TAKAHASHI, publishedon Nov. 15, 1989, CQ Publishing Co., Ltd., Japan. The combined magnetic head is comprised of a read/write core 1, an erase core 2, a read/write gap 3, an erase gap 4, a read/write coil 5 wound around the read/write core 1, and an erase coil 6 wound around the erase core 2. Also, the read/write core 1 and the read/write coil. 5 constitute a read/write head, and the erase core 2 and the erase coil 6 constitute an erase head.
FIG. 18 is an enlarged view showing a disk contact surface of the combined magnetic head shown in FIG. 17. The combined magnetic head of 3.5 inches, 1 Mbyte has dimensions concerning the read/write gap 3 and the erase gap 4 such as a read/write gap length of 1.5 .mu.m, an erase gap length of 2.5 .mu.m, a track width of 131 .mu.m of the read/write head, a track width of 71 .mu.m.times.2 of the erase head, and a gap distance of 590 .mu.m between two gaps with respect to one data track of the floppy disk drive.
FIGS. 19A and 19B and FIGS. 20A and 20B show a combined magnetic head of a double aizimuth system (gap surfaces of two magnetic heads are not parallel with each other and have an azimuth angle), to be used as a magnetic head of a VCR different from the tunnel erase system, as disclosed in, for example, "Magnetic Head Technique", Trikeps Co., Ltd. FIGS. 19A and 20A are elevational views seen from the tape slide surface side, and FIGS. 19B and 20B are front views. This combined magnetic head comprises a magnetic head 7 having a read/write gap 9a for a long time period recording mode (EP mode) and a magnetic head 8 having a read/write gap 9b for a short time period recording mode (SP mode). In this case, a large different point between the two magnetic heads 7 and 8 is that a track width for read/write of the EP mode magnetic head 7 is narrower than that of the SP mode magnetic head 8.
Next, the operation of the combined magnetic head of the tunnel erase system shown in FIGS. 17 and 18 will now be described. The combined magnetic head acts as an electromagnetic transducer or a magnetoelectric transducer for performing a recording and reproducing of magnetic information against a plurality of data tracks of a magnetic recording medium in a floppy disk drive.
First, at writing time when the combined magnetic head acts as the electromagnetic transducer, the floppy disk drive flows a current corresponding to a data signal of writing information to the read/write coil 5 of the combined magnetic head so as to generate a strong magnetic field near the read/write gap 3 according to the current value. By this magnetic field, the magnetic recording medium of the magnetic disk surface is magnetized to carry out the writing of the data signal thereon.
Next, at reading time when the combined magnetic head acts as the magnetoelectric transducer, the magnetic flux of the magnetic recording medium magnetized as described above interlinks with the read/write coil 5 to induce a voltage in the read/write coil 5, and at this time, a current flowing in the read/write coil 5 is picked up to perform the reading of the recording information.
Assuming that the magnetic head is always located in the center of the data track and there is no position shift (off-track) of the magnetic head in the reading processing, it is sufficient to provide only the read/write head for the magnetic head and no erase head is required. However, actuality, the magnetic head usually is somewhat off-track from the center of the track. Accordingly, in order to ensure a guard band between the data recorded on the adjacent data tracks even when the off-track is generated, the erase head is provided in rear of the read/write head. Further, after the data are flrstly written on the data track at the read/write gap 3, a trimming erasing is usually carried out at the erase gap 4.
In turn, as the technique for obtaining a large capacity (high density) of the floppy disk drive, there are two methods, that is, (1) by raising the track density on the magnetic recording medium surface, the number of the tracks is increased, and (2) by raising the line recording density (bit density), the number of the bits to be recorded on one track is increased.
In order to increase the track density, as a countermeasure of the off-track in which the magnetic head is somewhat shifted from the center of the track, it is insufficient to execute a positioning of the head by an open loop system by means of a stepping motor used in a conventional floppy disk drive. Hence, a closed loop (track servo) system is used. That is, a servo signal as a special signal used for positioning the magnetic head is written on the magnetic recording medium, and the servo signal is then read out of the magnetic recording medium. Then, by this servo signal, the position of the head is always corrected and the head is controlled so as to be always positioned in the right position.
In the floppy disk drive using this system, of course, the erase head is not used. However, when an overwrite characteristic of the floppy disk drive is attached much importance, for example, in case of using a barium ferrite medium having a bad overwrite performance, the erase head can sometimes be provided in front of the read/write head.
Further, when a floppy: disk drive having a large capacity due to the high track density is implemented, a problem arises, concerning compatibility with a conventional low density floppy disk drive. It is necessary for the magnetic head of the large capacity floppy disk drive to deal with both the high and low of the track density. In order to solve this problem, for example, in a floppy disk drive, as disclosed in Japanese Patent Laid-Open No. Sho 63-103408, a combined magnetic head composed of a low density magnetic head and a high density magnetic head arranged in parallel with each other at a predetermined interval is used.
Next, as to a VCR head used in the VCR for executing the recording and reproducing of image data against the magnetic recording medium in a similar manner to the floppy disk drive, a basic operational principle as an electromagnetic transducer and a magnetoelectric transducer is the same as the magnetic head of the floppy disk drive. In a usual VCR now in wide spread use, two magnetic heads for the wide and narrow track widths are used. In this case, when recording a high quality image, the writing and reading are carried out by the magnetic head for the wide track width, and, in case of a long time recording and reproducing with a small tape consumption amount, the magnetic head for the narrow track width is used to perform the recording and reproducing of the high track density.
In the VCR, of course, the off-track countermeasure is taken, and the closed loop system used in the large capacity floppy disk drive described above is frequently used. Thus, the servo signals for positioning the head are recorded on a video tape outside an image record area.
Further, as the prior art of the present invention, a variety of heads have been proposed, for example, a twin core head including two cores 12 composed of a ferrite and gaps 14, as shown in FIG. 45 and disclosed in Japanese Patent Laid-Open No. Sho 63-231711, a twin core head including two cores 12 of a ferrite material, a gap 14 and coils 16 wound around the cores 12, as shown in FIG. 46 and disclosed in Japanese Patent Laid-Open No. Sho 63-20709, a twin core head including two cores 12 made of a metal magnetic multi-layer film, a gap 14 and coils 16 wound around the cores 12, and as shown in FIG. 47 and disclosed in Japanese Patent Laid-Open No. Hei 3-71407, and a triple core head including three cores 12, a gap 14 and coils 16 wound around the cores 12, as shown in FIG. 50 and disclosed in Japanese Patent Laid-Open No. Hei 2-187909. These heads are all combined magnetic heads to be used in a magnetic recording system for recording data on a plurality of recording tracks via a guard band (unrecord area) or bands by a plurality of heads, as shown in a record magnetization pattern of the conventional magnetic heads in FIG. 48. The heads shown in FIGS. 45 to 47 have been proposed to consider the applying of the heads to an electronic still camera (video floppy), as described in their specifications. The guard band width of the electronic still camera is, for example, 40 .mu.m as described in "In-line Gap Thin Film Head For Metal Sheet", Magnetic Recording Workshop Document MR84-31, and to take the case of the head shown in FIG. 45, a width Wo corresponds to a guard band width of 40 .mu.m.
Also, the triple core combined magnetic head integrally composed of three magnetic heads as shown in FIG. 50 has been proposed for a recording system for recording the data on a plurality of tracks via the guard bands of the unrecord areas, as shown in a record magnetization pattern of the prior art in FIG. 51A.
As described above, in the magnetic recording system using the combined magnetic head composed of the read/write head and the erase head used in the open loop system of the conventional floppy disk drive, it is difficult to realize a large capacity floppy disk drive having a high track density and a high line recording density.
On the contrary, in the magnetic recording system of the closed loop system constituted by only the read/write head, it is necessary to provide a particular area for recording the servo signal for positioning of the head, and the data area is somewhat reduced accordingly.
Also, in the magnetic recording system using the combined magnetic head composed of the low density magnetic head and the high density magnetic head which are arranged in parallel with a predetermined interval therebetween in order to enable a lower compatibility in the large capacity floppy disk drive, the low density magnetic head and the high density magnetic head must be independently produced and are then combined with each other. Hence, the mass-productivity is low and the production cost is high.
Further, in case of the VCR head, the EP mode magnetic head and the SP mode magnetic head must be independently produced and are then combined with each other. Thus, the mass-productivity is low and the production cost is high.
Also, as to the multi track head of the electronic still camera or the like, a multi track recording via the guard bands is executed and the recording of the high track recording density can not be carried out.
Further, in the recording system where the data are recorded on the three recording tracks via the guard bands by using three magnetic heads at the same time, the high track density recording can not be performed.
Also, in a conventional magnetic head using a ferrite having a low saturation magnetic flux density and an inferior high frequency magnetic property as a core material, it is insufficient to perform a recording to a medium having a high coercive force represented by a metal medium suitable for the high density recording, and it is difficult to carry out a high frequency magnetic recording.